The biggest question is Jock, there's still an outside chance he re-signs though I wouldn't bet on it. If he does there's a bit more room to maneuver and we could probably focus on him with McCulloch and Murray as the backups.
Assuming he is gone though, we need someone ready to go at 15. McCulloch is still at least a year off being a viable option as a regular super starting 15, particularly after missing the whole season this year. There's an outside chance that either Flook or Murray could transition over the off season and be ready to go, but I'd want to have an alternative prepared if that was the aim.
In terms of potential signings, Glenn Vaihu looks like the only one I'd describe as anything like super rugby ready in Hospital's cup, but there are probably a few other guys who are ok as depth options. Further afield, Tom Banks is off contract but rumoured to be heading to Montpellier, and there's an outside chance James Ramm is off contract, but I think that's pretty unlikely at this stage. Isaac Lucas might also be off contract, but that's probably not happening without RA backing and I don't see the need at the national level. Otherwise it's a non-Australian option which should be fine from an RA perspective (there are heaps of qualified fullbacks signed to the other sides), but it's hard to know who that would be.
There's also a possibility of a Petaia return, but that is probably more likely for 2027. If that's looking more likely for 27 it wouldn't be the worst decision to either pay overs (within reason) to keep Campbell for another year. Even if lose Campbell it might be the case that we just bet on one of the current options (probably with Vaihu) to deliver, but there's some risk in that.